This invention relates to micromachined vacuum tube devices and, more particularly, to cold cathode vacuum tube devices and a method of making such devices.
The electronic era began with the invention of the vacuum tube. Computer and memory applications were limited by the lack of an available technology allowing for cost effective miniaturization of the vacuum tube. Vacuum tube technology was essentially replaced with the invention of the transistor and the subsequent development of low-cost batch fabrication techniques for solid state integrated circuits. It is now possible to integrate upwards of 10.sup.6 transistors onto a silicon chip. However, the relatively low mobility of silicon imposes a limit in switching speed upon the silicon technology using the metal-oxide-semi conductor field effect transistor (MOSFET). Furthermore, solid state devices are temperature sensitive and subject to radiation induced drifts, limiting silicon technology for certain military applications.
These limitations have been overcome somewhat with the development of alternate semi conductor devices made, for example, of gallium arsenide (GaAs). Gallium arsenide's mobility is approximately an order of magnitude greater than silicon's and GaAs devices exhibit better resistance to the effects of radiation.
Unfortunately, because of optical and acoustic phonon scattering at bias levels which are typically required for logic operations, the carrier velocity for all semi conductors saturates at approximately 2 to 3.times.10.sup.7 cm/sec (at room temperature). To reduce carrier transit time at a given saturation velocity, extensive research efforts are underway to shorten the distance between source and drain of the field effect transistor. Photolithography, materials, and cost limit the minimum gate dimensions achievable to about 0.5 micrometers.
Recently it has been suggested that vacuum devices can be made as small, and can be integrated to the same level, as solid state devices. R. Greene, H. Gray, and G. Campisi, "Vacuum Integrated Circuits", Technical Digest, International Electron Devices Meeting, Washington, D.C., Dec. 1-4, 1985, p. 172, IEEE, 85CH2252-5. Greene et al. describe two main approaches to vacuum integrated circuits (ICs): the thermionic IC and the field emitter IC. Although Greene et al. describe the concept of a basic field emitter tunneling triode, Greene et al. note that the field emitter IC faces difficulties with respect to fabrication techniques and fail to describe a method of making such a device.
Therefore, it is an object of the present invention to provide a method of making a field emitter or cold cathode vacuum device using solid state fabrication technology (micromachining).
It is another object of the present invention to describe a cold cathode vacuum device having a micromachined vacuum chamber.
Additional objects, advantages, and novel features of the invention will be set forth in the description which follows, and will become apparent in part to those skilled in the art upon examination of the following or may be learned by practice of the invention.